The invention relates in general to compressors and more specifically to an apparatus, system and method for minimizing resonant forces on an impeller of a compressor having a ported shroud.
Rotary compressors are used in a variety of applications for compressing gases. In turbochargers, for example, a rotating impeller within a housing sucks air through an intake port, compresses it in an intake passage and diffuses it in a volute housing. The compressed air is supplied to the intake manifold of an internal combustion engine. The operating range of a compressor extends from a surge condition, occurring at low airflow rates, to a choke condition experienced at high airflow rates. “Surging” occurs when a compressor operates at relatively low flow rates and the flow of air throughout the compressor begins to pulsate. As the airflow rate approaches relatively high volumes, such as when the velocity of the flow approaches the speed of sound, the compressor performance is reduced and choking occurs.
In order to improve the operating flow range, some compressors include drilled ports or openings on the inner wall of the intake passage, also referred to as a shroud, surrounding the impeller. These bypass ports reduce surging by reintroducing the air into the intake port through the bypass ports during low airflow rates.
Conventional compressors utilizing bypass ports or ported shrouds are limited, however, in that the impeller is exposed to cyclic stresses during high-airflow operation. At certain rotational speeds, air flowing through the diversion ports produces resonant forces on the blades of the impeller. The resonant forces may lead to immediate damage of the compressor or at least contribute to wear on compressor components that leads to eventual failure. Some attempts to reduce the resonant forces include asymmetrically spacing the openings forming the bypass ports. The impellers within these designs, unfortunately, still experience the resonant, cyclic forces.
Accordingly, there is a need for an apparatus, system, and method for minimizing resonant forces in compressors at high airflow rates.